Electrostatic chucking stage and substrate processing apparatus

ABSTRACT

This application discloses the structure of an ESC stage where a chucking electrode is sandwiched by a moderation layer and a covering layer. The moderation layer and the covering layer have the thermal expansion coefficients between the dielectric plate and the chucking electrode. This application also discloses the structure of an ESC stage where a chucking electrode is sandwiched by a moderation layer and a covering layer, which have internal stress directed oppositely to that of the chucking electrode. This application further discloses a substrate processing apparatus for carrying out a process onto a substrate as the substrate is maintained at a temperature higher than room temperature, comprising the electrostatic chucking stage for holding the substrate during the process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrostatic chucking (ESC) stage forholding a board-shaped object such as a substrate, and a substrateprocessing apparatus comprising the ESC stage.

2. Description of the Related Art

The ESC stages for chucking substrates by electrostatic force are usedwidely in the field of substrate processing. In manufacturing electronicdevices such as LSIs (Large-Scale Integrate circuits) and displaydevices such as LCDs (Liquid Crystal Displays), for example, there aremany steps of processing substrates that are bases for products. Inthese steps, ESC stages are used for securing process uniformity andprocess reproducibility. Taking the plasma etching as an example, asubstrate is etched, utilizing functions of ions and activated speciesproduced in plasma. In this, an ESC stage is used for holding thesubstrate at an optimum position against the plasma.

Generally, an ESC stage comprises a chucking electrode to which voltagefor chucking is applied, and a dielectric plate that is polarized by thevoltage applied to the chucking electrode. The held substrate is incontact with the dielectric plate, and chucked by static electricityinduced on the surface of the dielectric plate.

ESC stages are demanded to chuck substrates with making them stable. Ifa substrate is displaced or changes the posture on an ESC stage while aprocess is carried out, it might bring the problem of degrading theprocess uniformity and the process reproducibility. Thermaltransformation and thermal expansion of an ESC stage could be criticalin substrate processing in view of process homogeneity and processreproducibility. Temperatures of substrates during processes are oftenhigher than room temperature. This is usually from process conditions,otherwise because of environments in process chambers in which processesare carried out. Anyway, when temperature of a substrate rises up,temperature of the ESC stage rises up as well. If thermal transformationor thermal expansion of the ESC stage takes place from the temperaturerise, the held substrate might be transformed or displaced.

SUMMARY OF THE INVENTION

The invention of this application is to solve the above describedsubjects, and has the advantage of presenting a high-performance ESCstage capable of preventing transformation and displacement of a heldsubstrate. Concretely, the invention presents the structure of an ESCstage where a chucking electrode is sandwiched by a moderation layer anda covering layer. The moderation layer and the covering layer have thethermal expansion coefficient between the dielectric plate and thechucking electrode. The invention also presents the structure of anotherESC stage where a chucking electrode is sandwiched by a moderation layerand a covering layer, which have internal stress directed oppositely tothat of the chucking electrode. This invention also presents a substrateprocessing apparatus for carrying out a process onto a substrate as thesubstrate is maintained at a temperature higher than room temperature,comprising an ESC stage for holding the substrate during the process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic front cross-sectional view of the ESC stage as theembodiment of the invention.

FIG. 2 schematically explains the advantage of the ESC stage shown inFIG. 1.

FIG. 3 is a schematic front cross-sectional view of the substrateprocessing apparatus as the embodiment of the invention.

FIG. 4, FIG. 5, FIG. 6 and FIG. 7 schematically show the result of anexperiment for confirming the effect obtained from the structure of theembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of this invention will be described asfollows. First, the ESC stage of the embodiment will be described. FIG.1 is a schematic front cross-sectional view of the ESC stage of theembodiment. The ESC stage comprises a main body 41, a dielectric plate42 on which an object 9 is chucked, and a chucking electrode 43 to whichvoltage for chucking is applied.

The ESC stage is table-like as a whole, and holds the board-shapedobject 9 on the top surface. The main body 41 is made of metal such asaluminum or stainless-steel. The main body 41 is low column shaped. Thechucking electrode 43 is fixed on the main body 41. As shown in FIG. 1,the chucking electrode 43 has a flange-shaped part 431 at bottom end.This part 431 is hereinafter called “electrode flange”. The chuckingelectrode 43 is fixed on the main body 41 at the electrode flange 431 byscrewing. The chucking electrode 43 is electrically shorted with themain body 41.

A protection ring 49 is provided, surrounding the screwed electrodeflange 431. The protection ring 49 is made of insulator such as siliconoxide. The protection ring 49 is to protect the side of the chuckingelectrode 43 and the electrode flange 431 by covering them.

The dielectric plate 42 is located at the upside of the chuckingelectrode 43. As shown in FIG. 1, the chucking electrode 43 is formed ofan upward convex part and a flange-like part surrounding the convexpart. The dielectric plate 42 is almost the same in diameter as thechucking electrode 43.

A chucking power source 40 is connected with the above-described ESCstage. The type of the chucking power source 40 depends on that of theelectrostatic chucking. The ESC stage of this embodiment is themono-electrode type. A positive DC power source is adopted as thechucking power source 40. The chucking power source 40 is connected withthe main body 41, applying the positive DC voltage to the chuckingelectrode 43 via the main body 41. The applied voltage to the chuckingelectrode 43 causes dielectric polarization, which enables to chuck theobject 9. In this embodiment, because the positive DC voltage isapplied, positive charges are induced on the surface of the dielectricplate 42, thereby chucking the object 9 electro-statically.

Two mechanisms of the electro-static chucking have been known. One is byCoulomb force, and the other one is by Johnson-Rahbeck force.Johnson-Rahbeck force is the chucking force generated by convergence ofcurrents at micro-regions. The surfaces of the dielectric plate 42 andthe objects 9 are microscopically uneven. Micro-protrusions on the bothsurfaces contact with each other. When the electrostatic charges areinduced by the chucking power source 40, the flowing currents convergeat the protrusions contacting with each other, thereby generating theJohnson-Rahbeck force. The Johnson-Rahbeck force is dominant in such anESC stage as this embodiment. Still, the present invention is notlimited to the one where the Johnson-Rahbeck force is dominant.

One of points greatly characterizing the ESC stage of this embodiment isin the structure where thermal displacement and thermal transformationof the object 9 are effectively prevented. This point will be describedas follows. The ESC stage of this embodiment is supposedly used at a hottemperature environment. This would happen in case, for example, theobject 9 is subjected to a test under a hot temperature environment,other than the case that the object 9 is a substrate to be processed, asdescribed later. In the ESC stage of this embodiment, thermaldisplacement and thermal transformation are prevented even if it is usedat a high-temperature environment.

Concretely, as shown in FIG. 1, a moderation layer 44 is providedbetween the dielectric plate 42 and the chucking electrode 43. Themoderation layer 44 moderates difference of the thermal expansioncoefficients between the dielectric plate 42 and the chucking electrode43 so that thermal displacement and thermal transformation of the object9 can be prevented. More concretely, the moderation layer 44 has anintermediate value of the thermal expansion coefficient between that ofthe dielectric plate 42 and that of the chucking electrode 43.“Intermediate value of the thermal expansion coefficient” just means: ifthe thermal expansion coefficient of the chucking electrode 43 is higherthan the dielectric plate 42, then it is lower than the chuckingelectrode 43 and higher than the dielectric plate 42; and if the thermalexpansion coefficient of the dielectric plate 42 is higher than thechucking electrode 43, then it is lower than the dielectric plate 42 andhigher than the chucking electrode 43.

In this embodiment, specifically, the chucking electrode 43 is made ofaluminum, and the dielectric plate 42 is made of magnesia (MgO). Themoderation layer 44 is made of composite of ceramic and metal. Ascomposite having the thermal expansion coefficient between aluminum andmagnesia, we can name composite of silicon carbide and aluminum, whichhereinafter called “SiC—Al composite”. The thermal expansion coefficientof aluminum is 0.237×10⁻⁴/K, and that of magnesia is 14×10⁻⁶/K. In thiscase, the SiC—Al composite having the thermal expansion coefficient ofabout 10×10⁻⁶/K is preferably chosen as material of the moderation layer44. This kind of SiC—Al composite is manufactured by poring meltingaluminum into porous SiC bulk and fill out it. The porous SiC bulk isprepared by the hot-temperature high-pressure sinter-molding of SiCpowder. After cooling pored aluminum, the moderation layer 44 shaped asin Fin. 1 is obtained by such machine work as cutting. The volumeopening ratio of the porous SiC—Al bulk is adjusted by choosing anadequate temperature and an adequate pressure in the sinter-molding,which enables to adjust the volume of filled aluminum. The volumeopening ratio is obtained by comparing density of the porous bulk withthat of a non-porous one of the same size. The thermal expansioncoefficient of the SiC—Al composite manufactured in the described mannerdepends on the component ratio of aluminum against SiC. The describedthermal expansion coefficient of 10×10⁻⁶/K is obtained by adjusting thecomponent ratio.

In addition in the ESC stage of this embodiment, a covering layer 45 isprovided on the chucking electrode 43 at the opposite side to themoderation layer 44. In other words, the ESC stage has the structurewhere the chucking electrode 43 is sandwiched by the moderation layer 44and the covering layer 45. The covering layer 45 is inserted between thechucking electrode 43 and the main body 41. This covering layer 45 isalso made of material of which thermal expansion coefficient is betweenthe dielectric plate 42 and the chucking electrode 43. This is enabledby adopting the same material as of the moderation layer 44. Still,different material may be adopted for the covering layer 45.

The structure where the chucking electrode 43 is sandwiched by themoderation layer 44 and the covering layer 45 having the in-betweenthermal-expansion-coefficient enables to prevent displacement andtransformation of the chucked objected 9. This point will be describedin detail as follows, referring FIG. 2. FIG. 2 schematically explainsthe advantage of the ESC stage shown in FIG. 1.

Generally, there is large difference of the thermal expansioncoefficients between material of the chucking electrode, i.e. metal, andmaterial of the dielectric plate 42, i.e. dielectric. In the prior-artstructure where the dielectric plate 42 is fixed on the chuckingelectrode 43, when the ESC stage is heated up to a hot temperature,large transformation of the chucking electrode 43 would take placeeasily from its thermal expansion difference from the dielectric plate42. As a result, the dielectric plate 42 would be also transformed to beconvex as shown in FIG. 2(1), or to be concave as shown in FIG. 2(2).Such a transformation of the dielectric plate 42 would bringdisplacement or transformation of the object 9 being chucked.

In the prior-art structure where the moderation layer 44 having thein-between thermal-expansion-coefficient is inserted between thedielectric plate 42 and the chucking electrode 43, the difference of thethermal expansion coefficients is moderated, thereby suppressingtransformation of the dielectric plate 42. From the research by theinventors, it has turned out that transformation of the dielectric plate42 is further suppressed when a layer similar to the moderation layer 44is provided at the opposite side in addition, as shown in FIG. 2(4).Though the reason of this has not been clarified completely, it isconsidered that thermal expansion at the both sides of the chuckingelectrode 43 would be in a balanced state when it is sandwiched by thelayers having the in-between thermal-expansion-coefficients. It isfurther considered that internal-stress of the chucking electrode 43would be balanced by the both-sides layers having the similar thermalexpansion coefficients.

Respecting to thermal stress, it also could be considered that thermalstress within the moderation layer 44 and the covering layer 45 wouldfunction so as to restrain the transformation of the chucking electrode43. For example, when the chucking electrode 43 would be transformed tobe convex upward, internal thermal stress of the moderation layer 44 andthe covering layer 45 could function so as to transform it in theopposite way, i.e. making it convex downward. In addition, it could takeplace that when compression stress is produced within the chuckingelectrode 43, tensile stress is produced within the moderation layer 44and the covering layer 45. Inversely, compression stress could beproduced within the moderation layer 44 and the covering layer 45 whentensile stress is produced within the chucking electrode 43. Generally,it can be expressed that the moderation layer 44 and the covering layer45 could have stress opposite against stress within the chuckingelectrode 43. “Opposite” in this does not always mean that stress isdirected completely to an opposite direction. Expressing by vectors,vectors of stress within the moderation layer 44 and the covering layer45 make an angle over 90 degrees against the vector of stress within thechucking layer 43.

Anyway, provision of the covering layer 45 further restrainstransformation of the chucking electrode 43 and the consequenttransformation of the dielectric plate 42. As a result, displacement andtransformation of the object 9 can be restrained as well. The point thatthe covering layer 45 has a similar thermal-expansion-coefficient doesnot means complete correspondence of the thermal expansion coefficient,but just means that the covering layer 45 is similar to the moderationlayer 44 in view of having the in-between thermal-expansion-coefficient.Although, the same ceramic-metal composite as of the moderation layer44, e.g. SiC-Al composite, may be employed as material of the coveringlayer 45. The composite for the covering layer 45 is conductive, havingsufficient metal content. This is not to insulate the chucking electrode43 from the main body 41.

Structure for fixing the dielectric plate 42 is also significant in viewof restraining transformation of the dielectric plate 42. If thedielectric plate 42 is fixed locally, e.g. by screwing, thermaltransformation of the dielectric plate 42 would be aggravated because itis in a state pinched at the fixation points and thermal conductivity isenhanced locally at the fixation points. In this embodiment, thedielectric plate 42 is in junction with the chucking electrode 43 bysuch brazing material as one of which main component is aluminum orindium. “Main component” here implies pure aluminum or pure indium, inaddition to one including some additive. For example, the junction isperformed by whole-surface brazing. Concretely, a thin sheet made ofaluminum or indium is inserted between the dielectric plate 42 and themoderation layer 44. By cooling them after heating them up a requiredhot temperature, the dielectric plate 42 is fixed with the moderationlayer 44. In this blazing, it is preferable that pressure ranging from 1MPa to 2 MPa is mechanically applied with the heating at a temperatureranging from 570° C. to 590° C., in view of enhancing the thermalcontact and the mechanical strength. Such the junction by brazingrestrains transformation of the dielectric plate 42 further effectively.It is also practical to braze the moderation layer 44 and the chuckingelectrode 43, and to braze the chucking electrode 43 and the coveringlayer 45, in the same way. The dielectric plate 42 and the moderationlayer 44 may be soldered by solder of which main component is tin orlead.

Next will be described the embodiment of the substrate processingapparatus of the invention. The apparatus of the present invention is toprocess a substrate, maintaining it at a temperature higher than roomtemperature. In the following description, a plasma etching apparatus isadopted as an example of substrate processing apparatuses. Also in thefollowing description, “object” is replaced with “substrate” that is thesub-concept of it.

FIG. 3 is a schematic front cross-sectional view of the substrateprocessing apparatus as the embodiment of the invention. The apparatusshown in FIG. 3 comprises a process chamber in which plasma etching iscarried out onto the substrate 9, a process-gas introduction line 2 tointroduce a process gas into the process chamber 1, a plasma generator 3to generate plasma in the process chamber 1 by applying energy to theintroduced process gas, and an ESC stage 4 to hold the substrate 9 bychucking it electro-statically at a position where the substrate 9 canbe etched by a function of the plasma. The ESC stage 4 is almost thesame as the described embodiment.

The process chamber is the air-tight vacuum vessel, which is pumped by apumping line 11. The process chamber 1 is made of metal such asstain-less steel and electrically grounded. The pumping line 11comprises a vacuum pump 111 such as dry pump and a pumping speedcontroller 112, thereby being capable of maintaining pressure in theprocess chamber 1 at 10−3 Pa to 10 Pa.

The process-gas introduction line 2 is capable of introducing theprocess gas for the plasma etching at a required flow-rate. In thisembodiment, such a reactive gas as CHF3 is introduced into the processchamber 1 as the process gas. The process-gas introduction line 2comprises a gas bomb filled with the process gas, and a feeding pipeinterconnecting the gas bomb and the process chamber 1.

The plasma generator 3 generates the plasma by applying radio-frequency(RF) energy to the introduced process gas. The plasma generator 3comprises an opposed electrode 30 facing to the ESC stage 4, and an RFpower source 31 to apply RF voltage to the opposed electrode 30. The RFpower source 31 is hereinafter called “plasma-generation source”.Frequency of the plasma-generation source 31 ranges from 100 kHz toseveral tens MHz. The plasma-generation source 31 is connected with theopposed electrode 30 interposing a matching circuit (not shown). Outputof the plasma-generation source 31 may range from 300 W to 2500 W. Theopposed electrode 30 is installed air-tightly with the process chamber1, inserting an insulator 32.

When the plasma-generation source 31 applies the RF voltage to theopposed electrode 30, an RF discharge is ignited with the introducedprocess gas by RF field provided in the process chamber 1. Through thedischarge, the process gas transits to the state of plasma. In case theprocess gas is fluoride, ions and activated species of fluorine orfluoride are profusely produced in the plasma. Those ions and speciesreach the substrate 9, thereby etching the surface of the substrate 9.

Another RF power source 6 is connected with the ESC stage 4, interposinga capacitor. This RF power source 6 is to make ions incident onto thesubstrate 9 efficiently. This RF power source 6 is hereinafter called“ion-incidence source”. When the ion-incidence source 6 is operated inthe state the plasma is generated, self-biasing voltage is provided tothe substrate 9. The self biasing voltage is negative DC voltage that isgenerated through the mutual reaction of the plasma and the RF wave. Theself-biasing voltage makes ions incident onto the substrate 9efficiently, thereby enhancing the etching rate.

In this embodiment, a correction ring 46 is provided with the ESC stage4. The correction ring 46 is installed on the flange part of thedielectric plate 42, being flush with the substrate 9. The correctionring 46 is made of the same or similar material as the substrate 9, e.g.silicon mono-crystal. The correction ring 46 is to preventnon-uniformity or non-homogeneity of the process at the periphery on thesubstrate 9. Temperature on the substrate 9 tends to be lower at theperiphery in comparison with the center, because of heat dissipationfrom the edge of the substrate 9. For solving this problem, thecorrection ring 46 made of the same or similar material as the substrate9 is provided surrounding the substrate 9 to compensate the heatdissociation. The plasma is sustained by ions and electrons releasedfrom the substrate 9 during the etching as well. The plasma densitytends to be lower at the space facing to the periphery of the substrate9, because a less number of ions and electrons are released, compared tothe center. When the correction ring 46 made of the same or similarmaterial as the substrate 9 is provided surrounding it, amount of ionsand electros supplied to the space facing the periphery of the substrate9 is increased, thereby making the plasma more uniform and morehomogeneous.

As described above, the ESC stage 4 comprises the protection ring 49.The protection ring 49 protects the side of the chucking electrode 43and the electrode flange from the damage by the plasma or discharge. Incase the substrate 9 is made of silicon, the silicon-oxide-madeprotection ring 49 reduces probability to contaminate the substrate 9even if it is etched.

The ESC stage 4 is installed with the process chamber 1, inserting aninsulator 47. The insulator 47 is made of material such as alumina,insulating the main body 41 from the process chamber 1 as well asprotecting the main body 41 from the plasma. For preventing leakage ofvacuum from the process chamber 1, vacuum seals such as O-rings areprovided between the ESC stage 4 and the insulator 47, and between theprocess chamber 1 and the insulator 47.

The apparatus of this embodiment comprises a temperature controller 5for controlling temperature of the substrate 9 during the process. Asdescribed, temperature of a substrate to be kept during a process, whichis hereinafter called “optimum temperature”, is often higher than roomtemperature. In the plasma etching, however, temperature of thesubstrate 9 easily exceeds the optimum temperature by receiving heatfrom the plasma. For solving this problem, the temperature controller 5cools the substrate 9 and controls temperature of it at the optimumvalue during the etching.

As shown in FIG. 3, the chucking electrode 43 has a cavity in itself.The temperature controller 5 circulates coolant through the cavity tocool the chucking electrode 43, thereby cooling the substrate 9indirectly. The cavity preferably has a complex configuration so thatarea for heat exchange by the coolant can be enlarged. For example, acavity having complex uneven walls is formed by making a couple ofcooling fin-plates face to each other with each fin staggered. Thetemperature controller 51 comprises a coolant feeding pipe 51 to feedthe coolant into the cavity, a coolant drainage pipe 52 to drain thecoolant out of the cavity, and a circulator 53 to circulate the coolantcontrolled at a required low temperature. As the coolant, Fluorinate(trademark of 3M Corporation) is employed, for example. The temperaturecontroller 51 cools the substrate 9 at a temperature ranging from 80° C.to 90° C. by circulating the coolant of 30° C. to 40° C.

The substrate processing apparatus comprises a heat-transfer gasintroduction line (not shown) to introduce a gas between the chuckedsubstrate 9 and the dielectric plate 42. The heat-transfer gasintroduction is to enhance heat transfer efficiency between the chuckedsubstrate 9 and the dielectric plate 42. The back surface of thesubstrate 9 and the top surface of the dielectric plate 42 are notcompletely planar, but rough microscopically. Heat transfer efficiencyis poor at spaces formed of the micro roughness on the surfaces, becausethose are at a vacuum pressure. The heat-transfer gas introduction lineintroduces a gas of high thermal conductivity, e.g. helium, into thespaces, thereby improving heat transfer efficiency.

The ESC stage 4 comprises lift pins 48 in the inside for accepting andreleasing the substrate 9. The lift pins 48 are elevated by an elevationmechanism (not shown). Though only one lift pin 48 appears in FIG. 3,three lift pins 48 are provided actually.

Next will be described operation of the substrate processing apparatusof this embodiment. After a transfer mechanism (not shown) transfers thesubstrate 9 into the process chamber 1, the substrate 9 is placed on theESC stage 4 by operation of the lift pins 48. With operation of thechucking power source 40, the substrate 9 is chucked on the ESC stage 4.The process chamber 1 has been pumped at a required vacuum pressure inadvance. In this state, the process-gas introduction line 2 is operatedto introduce the process gas at a required flow-rate. Then, theplasma-generation source 31 is operated, thereby generating the plasma.The etching is performed utilizing the plasma as described. Thetemperature controller 5 cools the substrate 9 at an optimumtemperature. During the etching, the ion-incidence source 6 is operatedfor enhancing the etching efficiency. After performing the etching for arequired period, operations of the process-gas introduction line 2, theplasma-generation source 31, and the ion-incidence source 6 are stopped.Then, operation of the chucking power source 40 is stopped, dissolvingthe chucking of the substrate 9. After the process chamber 1 is pumpedagain, the substrate 9 is transferred out of the process chamber 1 bythe transfer mechanism.

In the substrate processing apparatus, though the chucking electrode 43is heated higher than room temperature, its transformation is restrainedby the moderation layer 44 and the covering layer as described.Therefore, transformation of the dielectric plate 42, and displacementor transformation of the substrate 9 caused thereby are restrained aswell, Accordingly, the process uniformity and the process homogeneityare enhanced.

The advantage of the moderation layer 44 and the covering layer 45 torestrain the transformation is greatly remarkable in the structure wherethe correction ring 46 is provided. This point will be described indetail as follows. The correction ring 46 has the configurationessentially equivalent to extending the substrate 9 outward. Material ofthe correction ring 46 is the same as or similar to the substrate 9. Thecorrection ring 46 is provided on the flange part of the dielectricplate 42, and chucked on it as well as the substrate 9. Probability andvolume of transformation of the dielectric plate 42 would be greater atthe flange part comparatively, because the flange part is thin andperipheral. If displacement or transformation of the correction ring 46takes place from transformation of the dielectric part 42, the functionto compensate heat dissociation from the edge of the substrate 9 wouldbecome out of uniform. Moreover, heat contact of the correction ring 46onto the dielectric plate 42 would be worsened by the displacement orthe transformation, resulting in that temperature of the correction ring46 rises higher than the substrate 9. What is particularly serious isthat the heat-contact deterioration of the correction ring 46 onto thedielectric plate happens randomly. The function of the correction ring46 to heat the substrate 9 compensatively also becomes random when theheat-contact deterioration of the correction ring 46 becomes random.This leads to much deteriorating reproducibility of the temperaturecondition on the substrate 9 during the process.

In this embodiment, however, the correction ring 46 is hard to betransformed or displaced, because transformation and displacement of thedielectric plate 42 are restrained by suppressing transformation of thechucking electrode 43. Therefore, this embodiment is free from such theproblems as non-uniformity and non-reproducibility of the substratetemperature.

Next will be described the result of an experiment for confirming theeffect obtained from the structure of the embodiment. FIGS. 4 to 7schematically show the result of this experiment. In this experiment,transformation and displacement of the surface of the dielectric plate42 were measured under conditions of different temperatures or differenttemperature histories on the ESC stages. The transformation and thedisplacement are measured by a distance meter. Setting a reference levelabove the ESC stage, distance from each point on the surface of thedielectric plate 42 to the reference level is measured by the distancemeter for detecting height of each point.

FIG. 4 and FIG. 5 both show heights of points on the surface of theconvex part of the dielectric plate 42. FIG. 4 shows the heights in caseof the prior-art ESC stage without the moderation layer 44 and thecovering layer 45. FIG. 5 shows the heights in case of the ESC stage ofthe described embodiment with the moderation layer 44 and the coveringlayer 45. FIG. 6 and FIG. 7 both show heights of points on the surfaceof the flange part of the dielectric plate 42. FIG. 6 shows the heightsin case of the prior-art ESC stage without the moderation layer 44 andthe covering layer 45. FIG. 7 shows the heights in case of the ESC stageof the described embodiment with the moderation layer 44 and thecovering layer 45. Location of each point on the flange part designatedby {circle around (1)}, {circle around (2)}, {circle around (3)},{circle around (4)} in FIG. 6 and FIG. 7 is shown in FIG. 1 by the same{circle around (1)}, {circle around (2)}, {circle around (3)}, {circlearound (4)} respectively.

The experiment was carried out, varying temperature of the ESC stages.Temperature of an ESO stage is hereinafter called “stage temperature”.In FIGS. 4 to 7, “A” designates data measured at the stage temperatureof 20° C. after leaving the ESC stage at 20° C. for all night long. “B”designates data measured, keeping the stage temperature at 5° C. “C”designates data measured at the stage temperature of 20° C. aftercooling the ESC stage at 5° C. “D” designates data measured, keeping thestage temperature at 50° C. “E” designates data measured, forcedlycooling the ESC stage at 20° C. after making the stage temperature 50°C. Though the ESC stage 4 comprises openings for interior members suchas the lift pins 48, data at those openings are omitted in FIGS. 4 to 7.

Commonly in FIGS. 4 to 7, level of the dielectric plate 42 is higherwhen the stage temperature is higher. This results from thermalexpansion of the whole ESC stage 4, being natural in a sense. What isthe problem is that displacement or transformation of the dielectricplate 42 depends on values of the stage temperature or histories of thestage temperature.

Specifically, each line appearing in FIG. 5 is drawn through points onthe surface of the dielectric plate 42, which is hereinafter called“surface level distribution”. As shown in FIG. 5, the surface leveldistribution is elevated up and down, depending on the stage temperatureor the history of the stage temperature, as it keeps the same figure. Inshort, it is displaced in parallel. This supposedly demonstrates thedielectric plate 42 has not been transformed and has performed theuniform thermal expansion. In FIG. 4, contrarily, the surface leveldistribution is elevated up and down as it changes the figure, dependingon the stage temperature or the history of the stage temperature. Inshort, it is not displaced in parallel. This supposedly demonstratestransformation of the dielectric plate 42 has taken place. What is theproblem in particular that the surface level distribution changes thefigure, depending on the history of the stage temperature. As shown inFIG. 4, even in the measurements at the same stage temperature 20° C.,the surface level distribution draws different curves in case it wasleft at 20° C. all night long and in case it was decreased by the forcedcooling from 50° C.

The same analysis is applicable to the result at the flange part. Asshown in FIG. 6, in case that the moderation layer 44 and the coveringlayer 45 are provided, the surface level distribution is elevated up anddown, keeping the same figure. Contrarily, as shown in FIG. 7, in casethat the moderation layer 44 and the covering layer 45 are not provided,the surface level distribution is elevated, changing the figure. Also ateach different history of the stage temperature, the surface leveldistribution draws a different curve in FIG. 7.

The point that the surface level distribution depends on the temperaturehistories would bring a serious problem with respect to reproducibilityof the substrate processing. Substrate processing apparatuses fabricatedat manufactures' factories are installed into production lines and usedafter such works as delivery inspections. However, the temperaturehistories of the apparatuses until actual substrate processes areinitially started are not the same among the apparatuses. Even theapparatuses performing the same processes almost always submit thedifferent temperature histories through works such as deliveryinspections in the manufactures' factories and test operations at theusers' lines. Moreover, considering each by-piece process of substrates,a temperature history that the ESO stage has submitted until the processfor a substrate is carried may differ from another temperature historythat the ESO stage has submitted until the process for another substrateis carried out. For example, a temperature history that the ESC stagehas submitted while the by-piece processes are continuingly carried outdiffers from another temperature history of the ESC stage that isinitially used for the process of the first substrate. Such a situationhappens, for example, when operation of the apparatus is resumed aftersuspension for the maintenance.

The point that the surface level distribution depends on the history ofthe stage temperature means that the substrate 9 would be transformed ordisplaced depending on the history, even if the ESC stage 4 iscontrolled at a constant temperature by the temperature controller 5.This could be the serious problem with respect to the processreproducibility. In case the moderation layer 44 and the covering layer45 are provided, however, the surface level distribution does not dependon the history of the stage temperature, with no transformation and nodisplacement of the substrate 9. Therefore, processes with highreproducibility are enabled only by maintaining the ESC stage 4 at arequired temperature.

More-detailed examples belonging to the embodiment will be described asfollows.

EXAMPLE 1

-   -   Material of Chucking Electrode 43: Aluminum    -   Material of Dielectric Plate 42: Magnesia (MgO)    -   Fixation of Dielectric Plate 42: Brazing by Al at 550° C.    -   Material of Moderation Layer 44: SiC—Al composite    -   Thickness of Moderation Layer 44: 1.2 mm    -   Material of Covering Layer 45: SiC—Al composite    -   Thickness of Covering Layer 45: 1.2 mm    -   Chucking Voltage: 500V

EXAMPLE 2

-   -   Material of Chucking Electrode 43: Aluminum    -   Material of Dielectric Plate 42: Alumina (Al₂O₃)    -   Fixation of Dielectric Plate 42: Brazing by In at 120° C.    -   Material of Moderation Layer 44: SiC—Cu composite    -   Thickness of Moderation Layer 44: 1.2 mm    -   Material of Covering Layer 45: SiC—Cu composite    -   Thickness of Covering Layer 45: 1.2 mm    -   Chucking Voltage: 500V

In the EXAMPLE 2, “SiC—Cu composite means composite” made of siliconcarbide and cupper. Manufacture of this composite may be the sameprocess as of the described SiC—Al composite. Magnesia is superior toalumina in erosion resistance. In case an erosive gas is used as in theetching, the dielectric plate 42 made of magnesia is more preferable.Size of the substrate 9 chucked by any one of the examples is, forexample, 300 mm diameter.

Material of the moderation layer 44 and the covering layer 45 is notlimited to described SiC—Al composite or SiC—Cu composite. It may beanother composite of ceramic and metal. For instance, it may becomposite of silicon carbide and nickel, composite of silicon carbideand Fe—Ni—Co alloy, composite of silicon carbide and Fe—Ni alloy,composite of silicon nitride (Si₃N₄) and nickel, or composite of siliconnitride and Fe—Ni alloy. Moreover, material of moderation layer 44 andthe covering layer 45 is not limited to composite of ceramic and metal.What is required is only that it has the thermal expansion coefficientbetween the chucking electrode 43 and the dielectric plate 42.

There are several types of electrostatic chucking such as thebi-electrode type and the multi-electrode type, in addition to thedescribed mono-electrode type. The bi-electrode type comprises a coupleof chucking electrodes, to which voltages of opposite polarity to eachother are applied. The multi-electrode type comprises multiple couplesof chucking electrodes, applying voltages of opposite polarity to eachelectrode of each couple. In these types, the chucking electrodes may beburied within the dielectric plate 42. In case of the mono-electrodetype, negative DC voltage may be applied for chucking. The presentinvention is also enabled in these types. Though the described ESC stagechucks the object or substrate 9 on the top surface, it may beoverturned, i.e. chucking the object or substrate 9 at the bottomsurface. Moreover, the ESC stage may chuck the object or substrate 9 onthe side surface, making it uprightly.

Though the plasma etching apparatus was adopted as the example ofsubstrate processing apparatuses in the above description, the presentinvention is enabled for other apparatuses such as plasma chemical vapordeposition (CVD) apparatuses and sputtering apparatuses. The temperaturecontroller 5 may heat the substrate 9 and maintain it at a requiredtemperature. There are many other applications of the ESC stage thansubstrate processing, for example a test of an object such as anenvironmental testing apparatus.

1. An electrostatic chucking stage for electro-statically chucking anobject, comprising: a dielectric plate on which the object is chucked; achucking electrode to which voltage for dielectrically polarizing thedielectric plate is applied; a moderation layer provided between thedielectric plate and the chucking electrode, and having a thermalexpansion coefficient between a thermal expansion coefficient of thedielectric plate and a thermal expansion coefficient of the chuckingelectrode; a covering layer provided on the chucking electrode at a sideopposite to the dielectric plate so that the chucking electrode issandwiched by the moderation layer and the covering layer, said coveringlayer having a thermal expansion coefficient between the thermalexpansion coefficient of the dielectric plate and the thermal expansioncoefficient of the chucking electrode; and wherein the moderation layerand the covering layer have structures comprising metal filled intoporous bulks made of ceramic, wherein the thermal expansion coefficientsof the moderation layer and the covering layer are obtained by adjustingvolume opening ratios of the porous bulks, wherein the chuckingelectrode has a flange part at a periphery thereof and is fixed to ametallic main body by screwing at the flange part, and the coveringlayer is inserted between the chucking electrode and the main body in aninterfacial recess inner to the flange part, wherein the moderationlayer and the covering layer are separated so as not to cover an end ofthe electrode, and wherein the electrode and the metallic main body areelectrically conducted through the metal filled into the porous ceramicof the covering layer to apply the voltage for chucking without aconnecting line through the covering layer.
 2. An electrostatic chuckingstage for electro-statically chucking an object as claimed in claim 1,wherein the dielectric plate is made of magnesia, the chucking electrodeis made of aluminum, and the moderation layer and the covering layer aremade of composite of aluminum and ceramic.
 3. An electrostatic chuckingstage for electro-statically chucking an object as claimed in claim 2,wherein the dielectric plate and the moderation layer are brazed with abrazing material containing aluminum as a main component.
 4. Anelectrostatic chucking stage for electro-statically chucking an objectas claimed in claim 2, wherein the dielectric plate and the moderationlayer are soldered with solder containing tin as a main component.
 5. Anelectrostatic chucking stage for electro-statically chucking an objectas claimed in claim 2, wherein the dielectric plate and the moderationlayer are soldered with solder containing lead as a main component. 6.An electrostatic chucking stage for electro-statically chucking anobject as claimed in claim 1, wherein the dielectric plate is made ofalumina, the chucking electrode is made of aluminum, and the moderationlayer and the covering layer are made of composite of aluminum andceramic.
 7. An electrostatic chucking stage for electro-staticallychucking an object as claimed in claim 6, wherein the dielectric plateand the moderation layer are brazed with a brazing material containingindium as a main component.
 8. A substrate processing apparatus forprocessing onto a substrate as the substrate is maintained at atemperature higher than room temperature, comprising an electrostaticchucking stage as claimed in claim 1 for holding the substrate duringprocess.
 9. A substrate processing apparatus as claimed in claim 8,comprising a plasma generator for generating plasma at a space facingthe substrate, wherein the process utilizes the plasma.
 10. Anelectrostatic chucking stage for electro-statically chucking an object,comprising: a dielectric plate on which the object is chucked; achucking electrode to which voltage for dielectrically polarizing thedielectric plate is applied; a moderation layer provided between thedielectric plate and the chucking electrode, and having a thermalexpansion coefficient between a thermal expansion coefficient of thedielectric plate and a thermal expansion coefficient of the chuckingelectrode, said moderation layer having a peripheral side open forthermal expansion without being covered by the dielectric plate; acovering layer provided on the chucking electrode at a side opposite tothe moderation layer so that the chucking electrode is sandwiched by themoderation layer and the covering layer, said covering layer having athermal expansion coefficient between the thermal expansion coefficientof the dielectric plate and the thermal expansion coefficient of thechucking electrode; and a protection ring surrounding a peripheral sideof the chucking electrode, and being provided separately from thedielectric plate and the moderation layer, wherein the moderation layerand the covering layer have structures comprising metal filled intoporous bulks made of ceramic, wherein the thermal expansion coefficientsof the moderation layer and the covering layer are obtained by adjustingvolume opening ratios of the porous bulks, wherein the chuckingelectrode has a flange part at a periphery thereof and is fixed to ametallic main body by screwing at the flange part, and the coveringlayer is inserted between the chucking electrode and the main body in aninterfacial recess inner to the flange part, wherein the moderationlayer and the covering layer are separated so as not to cover an end ofthe electrode and so as to allow the electrode thermally expand at theend thereof, and wherein the electrode and the metallic main body areelectrically conducted through the metal filled into the porous ceramicof the covering layer to apply the voltage for chucking without aconnecting line through the covering layer.
 11. An electrostaticchucking stage for electro-statically chucking an object as claimed inclaim 10, wherein the dielectric plate is made of magnesia, the chuckingelectrode is made of aluminum, and the moderation layer and the coveringlayer are made of composite of aluminum and ceramic.
 12. Anelectrostatic chucking stage for electro-statically chucking an objectas claimed in claim 11, wherein the dielectric plate and the moderationlayer are brazed with a brazing material containing aluminum as a maincomponent.
 13. An electrostatic chucking stage for electro-staticallychucking an object as claimed in claim 11, wherein the dielectric plateand the moderation layer are soldered with solder containing tin as amain component.
 14. An electrostatic chucking stage forelectro-statically chucking an object as claimed in claim 11, whereinthe dielectric plate and the moderation layer are soldered with soldercontaining lead as a main component.
 15. An electrostatic chucking stagefor electro-statically chucking an object as claimed in claim 10,wherein the dielectric plate is made of alumina, the chucking electrodeis made of aluminum, and the moderation layer and the covering layer aremade of composite of aluminum and ceramic.
 16. An electrostatic chuckingstage for electro-statically chucking an object as claimed in claim 15,wherein the dielectric plate and the moderation layer are brazed with abrazing material containing indium as a main component.
 17. A substrateprocessing apparatus for processing a substrate as the substrate ismaintained at a temperature higher than room temperature, comprising anelectrostatic chucking stage as claimed in claim 10 for holding thesubstrate during process.
 18. A substrate processing apparatus asclaimed in claim 17, comprising a plasma generator for generating plasmaat a space facing the substrate, wherein the process utilizes theplasma.
 19. An electrostatic chucking stage for electro-staticallychucking an object, the stage comprising: a dielectric plate forchucking the object; a chucking electrode for receiving a voltage fordielectrically polarizing the dielectric plate; a first layer providedbetween the dielectric plate and the chucking electrode, and having athermal expansion coefficient between a thermal expansion coefficient ofthe dielectric plate and a thermal expansion coefficient of the chuckingelectrode; a second layer provided on the chucking electrode so that thechucking electrode is sandwiched by the first layer and the secondlayer, the second layer having a thermal expansion coefficient betweenthe thermal expansion coefficient of the dielectric plate and thethermal expansion coefficient of the chucking electrode; and a main bodysupporting the second layer, wherein the first and second layers and themain body are electroconductive, and wherein for connecting electricalpower to the chucking electrode, an electrical power providing portionis connected to the main body, which conducts to the chucking electrodethrough the second layer.
 20. An electrostatic chucking stage forelectro-statically chucking an object according to claim 19 , whereinthe dielectric plate is made of magnesia, the chucking electrode is madeof aluminum, and each of the first layer and the second layer is made ofa composite of aluminum and ceramic.
 21. An electrostatic chucking stagefor electro-statically chucking an object according to claim 20 ,wherein the dielectric plate and the first layer are brazed with abrazing material containing aluminum as a main component.
 22. Anelectrostatic chucking stage for electro-statically chucking an objectaccording to claim 20 , wherein the dielectric plate and the first layerare soldered with solder containing tin as a main component.
 23. Anelectrostatic chucking stage for electro-statically chucking an objectaccording to claim 20 , wherein the dielectric plate and the first layerare soldered with solder containing lead as a main component.
 24. Anelectrostatic chucking stage for electro-statically chucking an objectaccording to claim 19 , wherein the dielectric plate is made of alumina,the chucking electrode is made of aluminum, and each of the first layerand the second layer is made of a composite of aluminum and ceramic. 25.An electrostatic chucking stage for electro-statically chucking anobject according to claim 24 , wherein the dielectric plate and thefirst layer are brazed with a brazing material containing indium as amain component.
 26. An electrostatic chucking stage forelectro-statically chucking an object, the stage comprising: adielectric plate for chucking the object; a chucking electrode forreceiving a voltage for dielectrically polarizing the dielectric plate;a first layer provided between the dielectric plate and the chuckingelectrode, and having a thermal expansion coefficient between a thermalexpansion coefficient of the dielectric plate and a thermal expansioncoefficient of the chucking electrode; a second layer provided on thechucking electrode so that the chucking electrode is sandwiched by thefirst layer and the second layer, the second layer having a thermalexpansion coefficient between the thermal expansion coefficient of thedielectric plate and the thermal expansion coefficient of the chuckingelectrode; and a main body supporting the second layer, wherein thefirst layer and the second layer have structures comprising metal filledinto porous bulks made of ceramic, wherein the thermal expansioncoefficients of the first layer and the second layer are obtained byadjusting volume opening ratios of the porous bulks, wherein the firstand second layers and the main body are electroconductive, and whereinfor connecting electrical power to the chucking electrode, an electricalpower providing portion is connected to the main body, which conducts tothe chucking electrode through the second layer.